Electrostatic chuck

ABSTRACT

An electrostatic chuck comprises: a dielectric substrate having a protrusion and a planar surface part. The protrusion is formed on a major surface of the dielectric substrate. An adsorption target material is mounted on the major surface. The planar surface part is formed in a periphery of the protrusion. The dielectric substrate is formed from a polycrystalline ceramics sintered body. A top face of the protrusion is a curved surface, and a first recess is formed in the top face to correspond to crystal grains that appear on the surface. The planar surface part has a flat part, and a second recess is formed in the flat part. A depth dimension of the first recess is greater than a depth dimension of the second recess. The electrostatic chuck can suppress the generation of particles and can easily recover a clean state of the electrostatic chuck surface.

TECHNICAL FIELD

An aspect of the invention generally relates to an electrostatic chuck.

BACKGROUND ART

Electrostatic chucks are used as means to adsorptively hold down anadsorption target material (such as a semiconductor wafer or a glasssubstrate) in substrate processing devices that perform etching,chemical vapor deposition (CVD), sputtering, ion implantation, ashing,exposure, inspection, and the like.

There is a risk here that particles will be generated if the adsorptiontarget material rubs against the mounting face of the electrostaticchuck. Further, increasing the contact surface area between the mountingface of the electrostatic chuck and the adsorption target material maylead to poor adsorption/desorption responsiveness of the adsorptiontarget material.

Therefore, techniques are known that improve adsorption/desorptionresponsiveness of the adsorption target material while suppressingparticle contamination by reducing the size of the contact surface areaby providing protrusions on the mounting face side of the electrostaticchuck.

Furthermore, in addition to providing protrusions on the mounting faceside of the electrostatic chuck, a technique is proposed for buffing thetop face of the protrusions to form a planar surface where the top facehas a surface roughness of not more than 0.25S (see Patent Literature1).

The technique disclosed in Patent Literature 1 mirror polishes the topface and side surface of the protrusions as well as the planar surfacearound the protrusions (bottom surface of the recess) such that thegeneration of particles can be suppressed even when the underside of theadsorption target material contacts these areas (see [0008], [0029], and[0035] of Patent Literature 1).

However, if the top face of the protrusion is made to be a planarsurface, particles may be increased instead due to the underside of theadsorption target material rubbing against the planar surface of the topface. Particularly in recent years, there has been a trend in which therestriction on the number of particles attached to the underside and thelike of the adsorption target material has become more strict leading toconcerns that flattening the top face of the protrusion can no longeraddress the restriction in the number of particles.

Note that flattening the top face of the protrusion may worsen theadsorption/desorption responsiveness of the adsorption target material.

Further, in addition to providing a protrusion on the mounting face sideof the electrostatic chuck, a technique is proposed for shot-blastprocessing the top face of the protrusion to form a rough surface regionin which the center line average roughness Ra on the top face is notless than 0.5 μm (see [0035] and [0043] for Patent Literature 2.

This rough surface region is provided to improve the uniformity of thein-plane temperature of the adsorption target material and to improvethe adsorption/desorption responsiveness of the adsorption targetmaterial. Further, because the rough surface region is a non-contactingface that does not contact the underside of the adsorption targetmaterial, rubbing between the rough surface region and the underside ofthe adsorption target material can be suppressed (see [0011] and [0014]of Patent Literature 2).

However, a smooth region is formed in which the center line averageroughness Ra around the rough surface region is not more than 0.5 μm. Inother words, similar to the technique disclosed in Patent Document 1,there is a risk of increasing the particles by the underside of theadsorption target material rubbing against the smooth region of the topface. Particularly in recent years, there has been a trend in which therestriction on the number of particles attached to the underside and thelike of the adsorption target material has become more strict leading toconcerns that providing a smooth region on the top face of theprotrusion can no longer address the restriction in the number ofparticles.

Note that providing a smooth region on the top face of the protrusionmay worsen the adsorption/desorption responsiveness of the adsorptiontarget material.

Further, when the protrusion is formed using a sand blast method or thelike, a defective part such as a crack may be generated in the surfaceregion of the protrusion or the surface region of the planar surfacepart. When these types of defective parts exist in the surface region, apart of the surface region desorbs as a base point of the defective partwith the risk of generating particles.

These types of defective parts that reside in the surface region cannotbe removed by buffing, and use of grinding processing methods, laserengraving methods, shot blasting methods, and the like have the risk offurther increasing defective parts.

Further, there is a risk of increasing particles if no consideration isgiven to the crystal grain diameter of the material that configures thetop face or side surface of the protrusion as well as the planar surfacepart in the periphery of the protrusion.

Further, if the rough surface region disclosed in Patent Document 2 isformed using a grinding processing method, laser engraving method, shotblasting method, and the like, thin and deep holes will be formed.Removing micro foreign objects trapped in this type of hole by cleaningis difficult, and there is a risk that a clean state of theelectrostatic chuck surface cannot be easily recovered.

The trapped micro foreign object may float up from the rough surfaceregion on account of an electric field generated at the time ofoperating the electrostatic chuck and it may adhere to the underside ofthe adsorption target material. In other words, because removing themicro foreign object trapped in the rough surface region is difficult bycleaning, any remaining foreign object may become a particle.

CITATION LIST Patent Literature

[PLT 1]

JP 2003-86664 A (Kokai)

[PLT 2]

JP 2001-341043 A (Kokai)

SUMMARY OF INVENTION Technical Problem

The aspect of the invention, based on recognition of such problems,provides an electrostatic chuck that can suppress the generation ofparticles and can easily recover a clean state of the electrostaticchuck surface.

Solution to Problem

The first invention is an electrostatic chuck that includes a dielectricsubstrate having a protrusion and a planar surface part. The protrusionis formed on a major surface of the dielectric substrate. An adsorptiontarget material is mounted on the major surface and the planar surfacepart is formed in a periphery of the protrusion. The dielectricsubstrate is formed from a polycrystalline ceramics sintered body, a topface of the protrusion is a curved surface where a first recess isformed in the top face to correspond to crystal grains that appear onthe surface, the planar surface part has a flat part, and a secondrecess is formed in the flat part, and a depth dimension of the firstrecess is greater than a depth dimension of the second recess.

With this electrostatic chuck, foreign objects trapped within the firstrecess and the second recess can be easily removed. In other words, theelectrostatic chuck surface can be easily recovered to a clean stateeven if foreign objects have adhered to the electrostatic chuck surface.

The top face is a curved surface where the first recess is formed.Therefore, the surface area of a contact portion between the top faceand the underside of the adsorption target material can be greatlyreduced. Micro foreign objects can also be captured within the firstrecess.

Because the second recess is formed in the flat part, the surface areaof the contact portion can be greatly reduced even if the underside ofthe adsorption target material contacts with the planar surface part asthe adsorption target material flexes. Micro foreign objects can also becaptured within the second recess.

In other words, reducing the surface area of the contact portion betweenthe underside of the adsorption target material can suppress thegeneration of particles. Further, capturing micro foreign objects in thefirst recess and the second recess can suppress the generation ofparticles.

The second invention, according to the first invention, is anelectrostatic chuck in which the top face has a curvature radius that isless than a curvature radius of a deformation curve of the adsorptiontarget material flexed by an adsorptive force.

With this electrostatic chuck, the shape of the top face can accommodatea flexed shape when the adsorption target material with a plate shapeundergoes electrostatic adsorption. Therefore, lowering the surfacepressure in the contact portion between the top face and the undersideof the adsorption target material, can suppress the generation ofparticles.

The third invention, according to the first invention, is anelectrostatic chuck in which the depth dimension of the first recess andthe depth dimension of the second recess are less than the average graindiameter of the crystal grains of the polycrystalline ceramics sinteredbody.

With this electrostatic chuck, the generation of particles can besuppressed in addition to easily recovering a clean state of theelectrostatic chuck surface.

The fourth invention, according to the first invention, is anelectrostatic chuck in which a side surface of the first recess is asloped face and an angle between a bottom surface of the first recessand the side surface of the first recess is an obtuse angle, and aportion where the side surface of the first recess meets the top faceand a portion where the side surface of the first recess meets thebottom surface of the first recess are shaped like a continualroundness.

With this electrostatic chuck, because the portion that becomes negativewhen cleaning the electrostatic chuck surface is eliminated, recovery ofa clean state of the electrostatic chuck surface can be more securelyand easily performed.

In other words, because the side surface portion of the first recesshaving a shallow depth is a continuous gentle shape, the contact areawith cleaning equipment, such as a nonwoven cloth, can be larger. Thus,micro foreign objects can be smoothly removed even when cleaning just bywiping with a nonwoven cloth that contains an organic solvent.

The fifth invention, according to the first invention, is anelectrostatic chuck in which a side surface of the second recess is asloped face and an angle between a bottom surface of the second recessand the side surface of the second recess is an obtuse angle, and aportion where the side surface of the second recess meets the flat partand the portion where the side surface of the second recess meets thebottom surface of the second recess are shaped like a continualroundness.

With this electrostatic chuck, because the portion that becomes negativewhen cleaning the electrostatic chuck surface is eliminated, recovery ofa clean state of the electrostatic chuck surface can be more securelyand easily performed.

In other words, because the side surface portion of the second recesshaving a shallow depth is a continuous gentle shape, the contact areawith cleaning equipment, such as a nonwoven cloth, can be larger. Thus,micro foreign objects can be smoothly removed even when cleaning just bywiping with a nonwoven cloth that contains an organic solvent.

The sixth invention, according to the first invention, is anelectrostatic chuck in which the planar surface part has a plurality ofholes that open on the planar surface part, and the flat part is formedin the periphery of the holes.

With this electrostatic chuck, because foreign objects can be capturedin a plurality of holes that open on the planar surface part, thegeneration of particles can be suppressed.

Further, the seventh invention, according to the sixth invention, is anelectrostatic chuck in which a depth dimension of the holes is less thanthe average grain diameter of the crystal grains of the polycrystallineceramics sintered body. With this electrostatic chuck, foreign objectstrapped within the holes can be easily removed.

The eighth invention, according to the first invention, is anelectrostatic chuck in which a height dimension of the protrusion islarger than the average grain diameter of the crystal grains of thepolycrystalline ceramics sintered body.

With this electrostatic chuck, changes in the shape of the protrusioncan be suppressed even if crystal grains of the polycrystalline ceramicssintered body are shed.

The ninth invention, according to the first invention, is anelectrostatic chuck in which the dielectric substrate is formed from apolycrystalline alumina sintered body and the average grain diameter isnot more than 1.5 μm, and the standard deviation of the grain diameterdistribution is not more than 1 μm.

With this electrostatic chuck, because the polycrystalline aluminasintered body that is the base material can be a dense configuration,the first recess and the second recess can be uniformly and stablyformed using a CMP method. As a result, the generation of particles canbe greatly reduced.

The 10th invention, according to the ninth invention, is anelectrostatic chuck in which the dielectric substrate has an aluminacontent of not less than 99.9 wt %, a bulk density of not less than3.96, and a volume resistivity of not less than 10¹⁴ Ωcm in an operatingtemperature range of the electrostatic chuck.

This type of electrostatic chuck adsorbs the adsorption target materialusing a Coulomb force. Although using a Coulomb force can generate astrong adsorptive force, the generation of particles can be greatlyreduced even with this type of electrostatic chuck.

The 11th invention, according to the first invention, is anelectrostatic chuck in which the curvature radius of the top face is notmore than 20 mm.

With this electrostatic chuck, the curvature radius of the top face canbe made to be less than the curvature radius of the deformation curve ofthe plate shaped adsorption target material flexed by the adsorptiveforce.

The 12th invention, according to the first invention, is anelectrostatic chuck in which the depth dimension of the first recess isnot less than 30 nm and not more than 150 nm, and the depth dimension ofthe second recess is not less than 5 nm and not more than 30 nm.

With this electrostatic chuck, foreign objects trapped within the firstrecess and the second recess can be easily removed. In other words, aclean state of the electrostatic chuck surface can be easily recoveredeven if foreign objects are adhered to the electrostatic chuck surface.

The 13th invention, according to the ninth invention, is anelectrostatic chuck in which the dielectric substrate has a volumeresistivity of not less than 10⁸ Ω·cm and not more than 10¹³ Ωcm in theoperating temperature range of the electrostatic chuck.

This type of electrostatic chuck adsorbs the adsorption target materialusing a Johnsen-Rahbeck force. Although using a Johnsen-Rahbeck forceprovides a stronger adsorptive force than when using a Coulomb force,the generation of particles can be greatly reduced even with this typeof electrostatic chuck.

The 14th invention, according to the 13th invention, is an electrostaticchuck in which the dielectric substrate has an alumina content of notless than 99.4 wt %. If formed from this type of highly pure alumina,contamination by substances other than alumina can be suppressed.

Advantageous Effects of Invention

According to the aspect of the invention, an electrostatic chuck thatcan suppress the generation of particles and that can easily recover aclean state of the electrostatic chuck surface can be provided.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1A is a schematic cross-sectional view for illustrating theelectrostatic chuck, and FIG. 1B is a schematic magnified view of the Apart in FIG. 1A.

FIG. 2 is a graph for illustrating the surface design andcross-sectional shape of the protrusion and the planar surface part.

FIG. 3 is a laser microscope photograph for illustrating the microrecess formed in the top face of the protrusion.

FIG. 4 is a scanning electron microscope photograph for illustrating themicro recess formed in the flat part.

FIG. 5 is a laser microscope photograph for illustrating when the topface is a flat face.

FIGS. 6A to 6C are diagrams for illustrating the shape of the recess 13a formed in the top face 3 a 1. FIG. 6A is a three-dimensional image ofthe recess 13 a, and FIGS. 6B and 6C are diagrams for illustrating theprofile of the recess 13 a.

FIGS. 7A to 7C are diagrams for illustrating the shape of the recess 13b formed in the flat part 3 b 2. FIG. 7A is a three-dimensional image ofthe recess 13 b, and FIGS. 7B and 7C are diagrams for illustrating theprofile of the recess 13 b.

FIG. 8 is a graph for illustrating the depth dimension of the holes thatopen in the planar surface part.

FIG. 9 is a laser microscope photograph for illustrating the dimensionof the length of the micro recess.

FIG. 10 is a laser microscope photograph for illustrating the dimensionof the crystal grains that appeared on the surface of thepolycrystalline ceramics sintered body.

FIG. 11 is a scanning electron microscope photograph for illustratingcracks generated in the surface region of the dielectric substrate.

FIG. 12 is a scanning electron microscope photograph for illustratingthe situation where a portion of the surface region is likely to desorb.

FIG. 13A is a laser microscope photograph for illustrating theinterference fringe that occurs in the portion where a defect resides,and FIG. 13B is a scanning electron microscope (SEM) photograph of thecross-section on the B-B line in FIG. 13A. Further, FIG. 13C is amagnified photograph of the D part in FIG. 13B and FIG. 13D is ascanning electron microscope photograph of the same portion as FIG. 13A.

FIG. 14A is a laser microscope photograph for illustrating theinterference fringe that occurs in the portion where a defect resides,and FIG. 14B is a scanning electron microscope photograph of thecross-section on the C-C line in FIG. 14A.

FIG. 15 is a photograph for illustrating the image that has been binarycoded processed.

FIG. 16 is a graph for illustrating the conditions for removingdefective parts using a CMP method.

FIG. 17 is a graph for illustrating the conditions prior to removingdefective parts using a CMP method.

FIG. 18 is a graph for illustrating the conditions for removingdefective parts using a CMP method.

FIG. 19 is a graph for illustrating the conditions prior to removingdefective parts using a CMP method.

FIG. 20A shows the case where the average grain diameter of the crystalgrains is approximately 1.8 μm, and FIG. 20B shows the case where theaverage grain diameter of the crystal grains is approximately 1.4 μm.

FIG. 21 is a photograph for illustrating the polycrystalline ceramicssintered body photographed by the laser microscope.

FIG. 22 is a graph for illustrating the average grain diameter of thecrystal grains and the standard deviation grain diameter distribution.

FIG. 23 is a graph for illustrating the average grain diameter of thecrystal grains and the standard deviation grain diameter distribution.

FIGS. 24A and 24B are diagrams for illustrating the dimension of thedepth of the micro recess. FIG. 24A is a graph for illustrating theprofile of the measurement value and FIG. 24B is a laser microscopephotograph for illustrating the measurement position.

FIG. 25 is a graph illustrating the relationship between the depthdimension of the micro recess 13 a formed in the top face 3 a 1 and thenumber of particles adhered to the underside of the adsorption targetmaterial.

FIG. 26A shows the case where the average grain diameter of the crystalgrains is between 20 μm and 50 μm, the bulk density is 3.7, and thealumina content is 90 wt %. FIG. 26B shows the case where the averagegrain diameter of the crystal grains is not more than 1.5 μm, the bulkdensity is 3.96, and the alumina content is 99.9 wt %.

FIGS. 27A and 27B are schematic diagrams for illustrating the number ofparticles adhered to the underside of a semiconductor wafer. Note thatFIG. 27A shows the case where the polycrystalline alumina sintered bodyserving as the base material is illustrated in FIG. 26A; and FIG. 27Bshows the case where the polycrystalline alumina sintered body servingas the base material is illustrated in FIG. 26B.

FIG. 28A is a schematic cross-sectional view for illustrating theelectrostatic chuck, and FIG. 28B is a schematic magnified view of the Fpart in FIG. 28A.

FIG. 29 is a flowchart for illustrating the manufacturing method of theelectrostatic chuck.

DESCRIPTION OF EMBODIMENTS

Hereinafter, embodiments of the invention will be described below withreference to the drawings. Note that the same numerals are applied tosimilar constituent elements in the drawings and detailed descriptionsof such constituent elements are appropriately omitted.

FIGS. 1A and 1B are schematic cross-sectional views for illustrating anelectrostatic chuck according to the embodiment. FIG. 1A is a schematiccross-sectional view for illustrating the electrostatic chuck, and FIG.1B is a schematic magnified view of the A part in FIG. 1A.

As shown in FIGS. 1A and 1B, a base 2, a dielectric substrate 3, and anelectrode 4 are provided on the electrostatic chuck 1.

An insulator layer 5 made of an inorganic material is formed on a firstmajor surface (the surface of the electrode 4 side) of the base 2. Thedielectric substrate 3 has a protrusion 3 a formed on a major surface ofthe side on which the adsorption target material is mounted (mountingface side) and a planar surface part 3 b formed in the periphery of theprotrusion 3 a. The top face of the protrusion 3 a becomes the mountingface when mounting the adsorption target material such as asemiconductor wafer. A detailed description will be given hereinafterconcerning the surface design and the cross-sectional shape of theprotrusion 3 a and the planar surface part 3 b.

A major surface of the dielectric substrate 3 on which the electrode 4is provided, and a major surface of the base 2 on which the insulatorlayer 5 is provided, are adhered by an insulating adhesive. Thisinsulating adhesive cures to become a bonding layer 6.

The electrode 4 and a power source 10 a and a power source 10 b areconnected by an electric wire 9. Although the electric wire 9 isprovided so as to pass through the base 2, the electric wire 9 and thebase 2 are insulated. FIGS. 1A and 1B illustrate a so-called bipolartype electrostatic chuck formed on the dielectric substrate 3 in whichthe positive and negative electrodes are mutually adjacent. However, itis not limited to this, and it may also be applied to a so-calledunipolar type electrostatic chuck in which a single electrode is formedon the dielectric substrate 3, and a tri-polar type and othermulti-polar types are also possible. The number, shape, and arrangementof electrodes can also be suitably modified.

A through hole 11 is provided so as to pass through the electrostaticchuck 1. A first end of the through hole 11 opens in the planar surfacepart 3 b, while a second end is connected to gas supply means (notillustrated) via pressure control means and flow control means (also notillustrated). The gas supply means (not illustrated) supplies heliumgas, argon gas, or the like. Furthermore, spaces 3 c provided by theformation of the planar surface part 3 b become the supply paths for thegas. The spaces 3 c respectively communicate with each other such thatthe supplied gas is diffused over the entirety.

Ring-form protrusions (not illustrated) may be provided in positions tosupport peripheral parts of the adsorption target material whenadsorption target material, such as a semiconductor wafer, is mounted,and the gas described above can also be provided so as to not leak out.If through holes other than the through holes 11 for the gas supplydescribed above are provided, then the ring-form protrusions (notillustrated) may be provided around the through holes thereof, and thegas described above can also be provided so as to not leak out.

The surface design and cross-sectional shape of this type of thering-form protrusions (not illustrated) may also be provided in asimilar manner as the protrusion 3 a.

In addition, not illustrated gas distribution channels (concave shapedgrooves) having a radial or concentric circular shape that communicateswith the through holes 11 may be provided in the planar surface part 3b. Providing this type of gas distribution channel may quicken the gasdistribution rate.

The base 2 may be formed of a metal having high thermal conductivitysuch as, for example, an aluminum alloy or copper. Furthermore, a fluidchannel 8 may be provided in which a cooling fluid or a heating fluidflows therein. The fluid channel 8 is not absolutely necessary but thatproviding such is preferred from the aspect of temperature control ofthe adsorption target material.

The insulator layer 5 provided on the first major surface of the base 2may be formed from a polycrystalline body such as alumina (Al₂O₃) oryttria (Y₂O₃) or the like. A configuration is preferred such that thethermal conductivity of the insulator layer 5 is greater than thethermal conductivity of the bonding layer 6. In this case, it ispreferred that the thermal conductivity of the insulator layer 5 is notless than 2 W/mK. By doing so, the heat transference becomes morefavorable than with the bonding layer alone, and thus the temperaturecontrollability of the adsorption target material and the uniformity ofthe in-plane temperature can be further improved.

A high thermal conductivity is preferred for the bonding layer 6. It ispreferred that the thermal conductivity be, for example, not less than 1W/mK and more preferably not less than 1.6 W/mK. This type of thermalconductivity can be obtained by adding, for example, alumina or aluminumnitride as a filler into a silicon resin or the like. Further, thethermal conductivity can be adjusted by the ratio of the additives.

The thickness of the bonding layer 6 is preferably to be as thin aspossible in consideration of heat transference. On the other hand, whenconsidering peeling of the bonding layer 6 due to heat shear stresscaused by the difference between the thermal expansion coefficient ofthe base 2 and the thermal expansion coefficient of the dielectricsubstrate 3, the thickness of the bonding layer 6 is preferably to be asthick as possible. Therefore, in consideration of this, the thickness ofthe bonding layer 6 is preferably to be not less than 0.1 mm and notmore than 0.3 mm.

Various materials can be used for the dielectric substrate 3 dependingon the various demands required by the electrostatic chuck. In thiscase, when considering the reliability of thermal conductivity andelectrical insulation, use of a polycrystalline ceramics sintered bodyis preferred. Examples of polycrystalline ceramics sintered bodiesinclude polycrystalline ceramic sintered bodies made of, for example,alumina, yttria, aluminum nitride, silicon carbide, and the like.

The volume resistivity of the material of the dielectric substrate 3 canbe not less than 10⁸ Ωcm in the operating temperature range of theelectrostatic chuck.

The volume resistivity in this specification is a value measured byusing the method indicated in the JIS Standard (JIS C 2141:1992 ceramicsmaterial test method for electrical insulation). The measurement in thiscase can be performed in the operating temperature range (for example,room temperature (approximately 25° C.)) of the electrostatic chuck.

The dielectric substrate 3 is preferably made from a polycrystallineceramics sintered body with an average grain diameter of the crystalgrains of not less than 0.8 μm and not more than 1.5 μm. The dielectricsubstrate 3 is more preferably made from a polycrystalline ceramicssintered body with an average grain diameter of the crystal grains ofnot less than 1 μm and not more than 1.5 μm. As long as a material madeof a polycrystalline ceramics sintered body with an average graindiameter of the crystal grains of not less than 0.8 μm and not more than1.5 μm is used, shedding of the crystal grains from the dielectricsubstrate 3 can be more securely suppressed. The changing of the shapeof the protrusion 3 a can be suppressed even if crystal grains are shed.A detailed description will be given hereinafter concerning the averagegrain diameter of the crystal grains of the polycrystalline ceramicssintered body that configures the dielectric substrate 3.

Examples of material for the electrode 4 include titanium oxide, thechemical element titanium or a mixture of titanium and titanium oxide,titanium nitride, titanium carbide, tungsten, gold, silver, copper,aluminum, chrome, nickel, a gold and platinum alloy, or the like.

Next, a description will be further given concerning the surface designand the cross-sectional shape of the protrusion 3 a and the planarsurface part 3 b. The top face of the protrusion 3 a becomes themounting face when mounting the adsorption target material. Therefore,conventionally, in order to reduce the generation of particles, the topface of the protrusion was a flat face while buffing and mirrorpolishing were performed such that micro-asperity was not formed in thetop face (for example, see Patent literature 1 and Patent literature 2).

However, as a result of the study by the inventors, it has becomeevident that making the top face of the protrusion to be a flat facesuch that micro-asperity is not formed in the top face instead leads toan increase in the number of particles.

Therefore, in the embodiment, a top face 3 a 1 of the protrusion 3 a isa curved surface while also forming a micro recess 13 a (first recess)on the top face 3 a 1 (See FIG. 2, FIG. 3 and FIG. 4).

The depth of the micro recess 13 a has a dimension based on the crystalgrain diameter. In this case, the depth dimension of the micro recess 13a is preferably not less than 30 nm and not more than 150 nm (see FIG.25).

Here, shapes that are close to the protrusion 3 a and the planar surfacepart 3 b are formed by using a sandblast method to erode away theperiphery of the portion that is to be the protrusion 3 a. Thus, in thismanner a plurality of holes 3 b 1 that open in the planar surface part 3b are formed in the planar surface part 3 b. As will be describedhereinafter, a flat part 3 b 2 is formed in the periphery of the openingof the hole 3 b 1 that opens in the planar surface part 3 b.

Furthermore, in the embodiment, a micro recess 13 b (second recess) isalso formed in the flat part 3 b 2.

The depth dimension of the micro recess 13 b is not more than 30 nm, andpreferably not more than 20 nm, and more preferably not less than 5 nmand not more than 20 nm.

FIG. 2 is a graph for illustrating the surface design andcross-sectional shape of the protrusion and the planar surface part.

FIG. 2 shows the results on measurement of the surface of the protrusionand the planar surface part using a contact type roughness meter.

As shown in FIG. 2, the top face 3 a 1 of the protrusion 3 a has acurved surface that projects toward the outer side. Furthermore, themicro recess 13 a is formed in the top face 3 a 1 of the protrusion 3 a.

A plurality of holes 3 b 1 that open in the planar surface part 3 b, andthe flat part 3 b 2 formed in the periphery of the opening of the holes3 b 1, are formed in the planar surface part 3 b. Furthermore, the microrecess 13 b is formed in the flat part 3 b 2.

Here, an explanation will be given for the “top face” in thisspecification.

As shown in FIG. 2, the term “top face” in this specification refers toa portion that is within the length of L2 equidistant from the centeraxis of the protrusion 3 a. Here, L2 is a length that is 80% of thelength L1 of the bottom of the protrusion 3 a.

As long as the top face 3 a 1 of the protrusion 3 a has a curvedsurface, the outer side of the top face 3 a 1 may be a curved surface orit may be a linear surface.

Next, an explanation will be given for the “curvature radius R” in thisspecification.

As shown in FIG. 2, the positions of both end portions of the top face 3a 1 are P1 and P3, and the center position (the intersecting pointposition of the top face 3 a 1 and the center axis of the protrusion 3a) of the top face 3 a 1 is P2. A radius of the circle that passesthrough P1, P2, and P3 is the “curvature radius R” of the curved surfacein this specification.

The center position of the circle that passes through P1, P2, and P3 isthe intersecting point of the perpendicular bisector of the line segmentthat connects P1 and P2 and the perpendicular bisector of the linesegment that connects P3 and P2. Therefore, the “curvature radius R” ofthe curved surface can be obtained by deriving the center position ofthe circle that passes through P1, P2, and P3 from the positions of P1,P2, and P3, and deriving the distance to any one of P1, P2, or P 3 fromthe center position of the circle.

According to the findings obtained by the inventors, the curvatureradius R of the top face 3 a 1 is preferably made to be less than thecurvature radius of the deformation curve of the plate shaped adsorptiontarget material flexed by the adsorptive force.

By doing so, the shape of the top face 3 a 1 can accommodate a flexedshape when the adsorption target material with a plate shape undergoeselectrostatic adsorption. Therefore, lowering the surface pressure inthe contact portion between the underside of the adsorption targetmaterial and the top face 3 a 1, can suppress the generation ofparticles.

In this case, if the curvature radius R is not more than 20 mm, then thecurvature radius of the top face 3 a 1 can be made to be less than thecurvature radius of the deformation curve of the plate shaped adsorptiontarget material flexed by the adsorptive force.

Next, an explanation will be given for the micro recess formed in thetop face 3 a 1 and flat part 3 b 2.

FIG. 3 is a laser microscope photograph for illustrating the microrecess formed in the top face of the protrusion.

FIG. 4 is a scanning electron microscope photograph for illustrating themicro recess formed in the flat part.

FIG. 5 is a laser microscope photograph for illustrating when the topface 3 a 1 is made into a flat part.

As shown in FIG. 3, the micro recess 13 a is formed in the top face 3 a1 of the protrusion 3 a.

As shown in FIG. 4, the micro recess 13 b is formed in the flat part 3 b2.

In FIG. 5, the micro recess 13 a is not formed in the top face 3 a 1.

In FIG. 3 and FIG. 4, the top face 3 a 1 is a curved surface with arecess 13 a is formed. Therefore, the surface area of the contactportion between the top face 3 a 1 and the underside of the adsorptiontarget material can be greatly reduced. Micro foreign objects can alsobe captured within the recess 13 a.

In contrast to this, because the micro recess 13 a is not formed in thetop face 3 a 1 as illustrated in FIG. 5, the surface area of the contactportion between the top face 3 a 1 and the underside of the adsorptiontarget material is larger. Micro foreign objects also cannot becaptured.

Because the recess 13 b is formed in the flat part 3 b 2, the surfacearea of the contact portion can be greatly reduced even if the undersideof the adsorption target material contacts the planar surface part 3 bas the adsorption target material flexes. Micro foreign objects can alsobe captured within the recess 13 b.

In other words, reducing the surface area of the contact portion betweenthe underside of the adsorption target material can suppress thegeneration of particles. Capturing micro foreign objects in the recess13 a and the recess 13 b can suppress the generation of particles.

Table 1 and Table 2 illustrate the results of suppressing the generationof particles.

Table 1 shows the examples illustrated in FIG. 3 and FIG. 4 while table2 shows the examples illustrated in FIG. 5.

In Table 1 and Table 2, the adsorption target material is asemiconductor wafer and the total number of particles adhered to theunderside of the semiconductor wafer is made up for each grain ofparticle.

The number of particles in Table 1 and Table 2 is the total number ofparticles in a predetermined area and converts such value to the numberof particles in the semiconductor wafer of a 300 mm diameter.

TABLE 1 0.15~0.2 0.2~0.3 0.3~0.5 0.5 μm or μm μm μm more total Afterwashing 50 56 27 79 212 After 10 times 25 18 25 47 115 adsorption After100 times 36 29 32 58 155 adsorption After 200 times 18 27 20 23 88adsorption After 300 times 29 16 14 16 75 adsorption After 400 times 2316 14 16 69 adsorption After 500 times 25 11 14 14 64 adsorption

TABLE 2 0.15~0.2 0.2~0.3 0.3~0.5 0.5 μm or μm μm μm more total Afterwashing 79 56 9 266 410 After 1 time 232 83 23 387 725 adsorption After5 times 140 45 11 263 459 adsorption After 10 times 122 56 9 257 444adsorption After 15 times 140 59 14 189 402 adsorption

As can be understood from Table 1, when a micro recess such as thatillustrated in FIG. 3 and FIG. 4 is formed, the electrostatic chucksurface is cleaned, the generation of particles can be suppressed evenwhen the electrostatic chuck surface is cleaned and thereafteradsorption of the semiconductor wafer is repeated.

The depth dimension of the recess 13 a formed in the top face 3 a 1 islarger than the depth dimension of the recess 13 b formed in the flatpart 3 b 2.

Furthermore, the surface area is wider and the depth is shallower withthe recess 13 a and the recess 13 b, and the side surface of the recess13 a and the recess 13 b is a sloped face.

Therefore, foreign objects trapped within the recess 13 a and the recess13 b can be easily removed. In other words, the electrostatic chucksurface can be easily recovered to a clean state even if foreign objectshave adhered to the electrostatic chuck surface.

In contrast to this, as can be understood from Table 2, when the microrecess is not formed as illustrated in FIG. 5 and the electrostaticchuck surface is cleaned, it stabilizes as is with a large number ofparticles if attempting to repeat adsorption of the semiconductor waferthereafter.

The detailed description will be given hereinafter concerning the depthdimension and the shape of the side surface of the recess 13 a and 13 b.

Table 3 and Table 4 illustrate the recovery of a clean state of theelectrostatic chuck surface.

Table 3 shows the examples illustrated in FIG. 3 and FIG. 4 while table4 shows the examples illustrated in FIG. 5.

In Table 3 and Table 4, the adsorption target material is asemiconductor wafer and the total number of particles adhered to theunderside of the semiconductor wafer is made up for each grain ofparticle.

The number of particles in Table 3 and Table 4 is the total number ofparticles in a predetermined area and converts such value to the numberof particles in the semiconductor wafer of a 300 mm diameter.

Further, “initial state” is when adsorption is performed on asemiconductor wafer while foreign objects are adhered on theelectrostatic chuck surface. Further, “No. 1 to No. 5” is when theelectrostatic chuck surface is cleaned and adsorption of thesemiconductor wafer is performed thereafter. Cleaning is performed bywiping the electrostatic chuck surface with a nonwoven cloth containingan organic solvent.

TABLE 3 0.15~0.2 0.2~0.3 0.3~0.5 0.5 μm or μm μm μm more total Initialstate 2455 2441 10676 15784 31356 No. 1 47 27 54 63 191 No. 2 56 25 3629 146 No. 3 34 29 34 32 129 No. 4 25 25 27 23 100 No. 5 11 14 9 11 45

TABLE 4 0.15~0.2 0.2~0.3 0.3~0.5 0.5 μm or μm μm μm more total Initialstate 1577 2084 9295 16135 29091 No. 1 146 79 54 303 582 No. 2 101 70 41299 511 No. 3 124 77 47 266 514 No. 4 100 69 40 200 409 No. 5 90 77 66184 417

As can be seen from No. 1 of Table 3, when a micro recess is formed suchas that illustrated in FIG. 3 and FIG. 4, the number of particlesadhered to the underside of the semiconductor wafer can be greatlyreduced even when cleaning the electrostatic chuck surface just bywiping with a nonwoven cloth that contains an organic solvent. Thismeans that the electrostatic chuck surface can be easily recovered to aclean state even if foreign objects have adhered to the electrostaticchuck surface.

The depth dimension of the recess 13 a and the depth dimension of therecess 13 b are less than the average grain diameter of the crystalgrains of the polycrystalline ceramics sintered body that configures thedielectric substrate 3.

By doing this, the generation of particles can be suppressed in additionto easily recovering a clean state of the electrostatic chuck surface.

The micro recesses 13 a and 13 b that will be described hereinafter areformed by using a CMP method to be described later.

FIGS. 6A to 6C are diagrams for illustrating the shape of the recess 13a formed in the top face 3 a 1. FIG. 6A is a three-dimensional image ofthe recess 13 a, and FIGS. 6B and 6C are diagrams for illustrating theprofile of the recess 13 a.

FIGS. 7A to 7C are diagrams for illustrating the shape of the recess 13b formed in the flat part 3 b 2. FIG. 7A is a three-dimensional image ofthe recess 13 b, and FIGS. 7B and 7C are diagrams for illustrating theprofile of the recess 13 b.

As shown in FIGS. 6A to 6C, a side surface of the recess 13 a is asloped face, and an angle between a bottom surface of the recess 13 aand the side surface of the recessed 13 a (angle of the sloped face) isan obtuse angle. A portion where the side surface of the recess 13 ameets the top face 3 a 1, and a portion where the side surface of therecess 13 a meets the bottom surface of the recess 13 a are shaped likea continual roundness.

As shown in FIGS. 7A to 7C, the side surface of the recess 13 b is asloped face, and the angle (angle of the sloped face) formed by thebottom surface of the recess 13 b and the side surface of the recessed13 b is an obtuse angle. The portion where the side surface of therecess 13 b meets the flat part 3 b 2 and the portion where the sidesurface of the recess 13 b meets the bottom surface of the recess 13 bare shaped like a continual roundness.

The obtuse angle in this specification is an angle that is greater than90 degrees but less than 180 degrees.

A shape like a continual roundness refers to rounding a corner bychemical erosion during the use of a CMP method to be described below,and is a state where the side surface of the recess 13 a meets the topface 3 a 1, and the portion where the side surface of the recess 13 ameets the bottom surface of the recess 13 a and where the side surfaceof the recess 13 b meets the flat part 3 b 2 and the portion where theside surface of the recess 13 b meets the bottom surface of the recess13 b to smoothly connect.

Therefore, because the portion that becomes negative when cleaning theelectrostatic chuck surface is eliminated, recovery of a clean state ofthe electrostatic chuck surface can be more securely and easilyperformed.

In other words, because the side surface portion of the recess 13 a andrecess 13 b having a shallow depth is a continuous gentle shape, thecontact area with cleaning equipment, such as a nonwoven cloth, can belarger. Thus, micro foreign objects can be smoothly removed even whencleaning just by wiping with a nonwoven cloth that contains an organicsolvent.

In contrast to this, as can be seen from Table 4, when a micro recess isnot formed such as that illustrated in FIG. 5, the number of particlescannot be greatly reduced when cleaning the electrostatic chuck surfacejust by wiping with a nonwoven cloth that contains an organic solvent.

In the electrostatic chuck 1 according to the embodiment, the portionwhere the side surface of the protrusion 3 a meets the top face 3 a 1and the portion where the side surface of the protrusion 3 a beats theplanar surface part 3 b are shaped like a continual roundness. In otherwords, the side surface of the protrusion 3 a and the top face 3 a 1 arecurved surfaces that smoothly connect; and the side surface of theprotrusion 3 a and the planar surface part 3 b are curved surfaces thatsmoothly connect.

(CMP Processing)

The recess 13 a and recess 13 b having the shapes described above cannotbe formed in to the top face 3 a 1 and the flat part 3 b 2 usingmechanical processing methods such as buffing, grinding processing,laser engraving, shot blasting, sand blasting, or the like. Further, theprotrusion 3 a having the shape described above cannot be formed usingthese mechanical processing methods.

Descriptions are given below of the formation methods of the protrusion3 a, planar surface part 3 b, flat part 3 b 2, hole 3 b 1, recess 13 a,recess 13 b, and the like.

First, shapes that are close to the protrusion 3 a and the planarsurface part 3 b are formed.

For example, the portion that will become the protrusion 3 a is masked,and shapes that are close to the protrusion 3 a and the planar surfacepart 3 b are formed by using a sandblast method to erode away theportion that is not masked. At this time, a plurality of holes 3 b 1that open in the planar surface part 3 b are formed in the planarsurface part 3 b. As long as this type of hole 3 b 1 is formed, foreignobjects can be captured in the plurality of holes thus suppressing thegeneration of particles.

In this case, the depth dimension of the holes 3 b 1 is preferred to beless than the average grain diameter (not less than 0.8 μm and not morethan 1.5 μm) of the crystal grains of the polycrystalline ceramicssintered body to be described below. With this type of shallow hole,foreign objects captured in the holes 3 b 1 can be easily removed. Adetailed description will be given hereinafter for the average graindiameter of the crystal grains of the polycrystalline ceramics sinteredbody.

FIG. 8 is a graph for illustrating the depth dimension of the holes 3 b1 that open in the planar surface part 3 b.

As shown in FIG. 8, the depth dimension of the holes 3 b 1 is less than1 μm, and crystal grains shed from the polycrystalline ceramics sinteredbody that have entered into the holes 3 b 1 can be easily removed. Thedepth dimension of the holes 3 b 1 can be controlled by the processingconditions (for example, the size of the grinding material used and thelike) in the sandblast method or the like.

Next, the mask is removed and the protrusion 3 a is processed into theshape described above. At this time, the flat part 3 b 2 is formed inthe periphery of the opening of the plurality of holes 3 b 1 that openin the planar surface part 3 b. Furthermore, the micro recess 13 adescribed above is formed in the top face 3 a 1 of the protrusion 3 a,and the micro recess 13 b described above is formed in the flat part 3 b2.

In this case, according to the findings obtained by the inventors, theprotrusion 3 a, the flat part 3 b 2, the recess 13 a, and the recess 13b can be formed in one step if a chemical mechanical polishing (CMP)method is used.

The CMP method is generally used when performing planarizationprocessing. Therefore, it would not be considered for forming theprotrusion 3 a having the shape such as that described above as well asbeing able to form the micro recesses 13 a and 13 b.

However, according to the findings obtained by the inventors, the microrecesses 13 a and 13 b can be formed if utilizing the active effect ofchemical components contained in slurry.

In other words, the micro recesses 13 a and 13 b can be formed ifutilizing the crystal orientation dependence relative to the etchingrate found in the polycrystalline ceramics sintered body. In otherwords, in the surface region of the polycrystalline ceramics sinteredbody, the micro recesses 13 a and 13 b can be formed because the areashaving crystal orientation for easy etching are etched first.

The protrusion 3 a and the flat part 3 b 2 can be formed by themechanical polishing effect due to the abrasive grains contained in theslurry, and by the chemical polishing effect due to the chemicalcomponents contained in the slurry. In this case, the flat part 3 b 2 isformed in the periphery of the holes 3 b 1.

Here, an illustration will be given of the process conditions for theCMP method.

A polishing cloth, such as a rigid polyurethane foam polishing cloth,can be used. A rotating speed of 60 RPM can be used for a grinder, and aload of 0.2 kg/cm² can be used. The abrasive grains contained in theslurry that can be used include SiO₂ (silicon oxide), CeO₂ (ceriumoxide), TiO₂ (titanium oxide), MgO (magnesium oxide), Y₂O₃ (yttriumoxide), and SnO₂ (tin oxide). Further, the ratio of abrasive grains toslurry can be approximately between 10 to 20 wt %. Examples of chemicalcomponents contained in the slurry that can be used include pHadjusters, dispersing agents for the abrasive grains, surfactants, andthe like. In this case, when considering crystal anisotropy etchingdescribed above, an alkaline slurry is preferred. Therefore, thehydrogen ion exponent of the slurry would be between approximately pH 8to 13. Note that the supplied amount of slurry can be, for example,approximately 20 cc per min.

Furthermore, according to the findings obtained by the inventors,processing time becomes an essential element.

In other words, with a short processing time it becomes a flatteningprocess and the protrusion 3 a having the shape described above cannotbe formed, and further, the micro recesses 13 a and 13 b cannot beformed. For example, a processing time of approximately several minutesis a flattening process.

On the other hand, with a short processing time of approximately severalhours, the protrusion 3 a having the shape described above can beformed, and further, the micro recesses 13 a and 13 b can be formed.

Because the top face 3 a 1 of the protrusion 3 a is easier to processthen the planar surface part 3 b, a relationship between the depthdimension of the recess 13 a described above and the depth dimension ofthe recess 13 b can be configured. In other words, the depth dimensionof the recess 13 a formed in the top face 3 a 1 can be made so as to begreater than the depth dimension of the recess 13 b formed in the flatpart 3 b 2.

The processing time described above can be appropriately modifiedaccording to such other processing conditions (for example, the hydrogenion exponent or the like of the slurry) in the CMP method.

Consideration can also be given to the interference fringe spaceoccupancy ratio to be described hereinafter. In other words, processingby the CMP method can be performed not only to form the recess 13 a andthe recess 13 b but also until the interference fringe space occupancyratio to be described hereinafter becomes less than 1%. A detaileddescription will be given hereinafter concerning the interference fringespace occupancy ratio and the like.

A height dimension of the protrusion 3 a can be made to be greater thanthe average grain diameter of crystal grains of the polycrystallineceramics sintered body to be described hereinafter. Or, the averagegrain diameter of crystal grains of the polycrystalline ceramicssintered body can be made to be less than the height dimension of theprotrusion 3 a.

By doing so, the shedding of crystal grains from the dielectricsubstrate 3 can be suppressed. Further, the changing of the shape of theprotrusion 3 a can be suppressed even if crystal grains are shed.

FIG. 9 is a laser microscope photograph for illustrating the measurementof the length of the micro recess.

FIG. 10 is a laser microscope photograph for illustrating themeasurement of the crystal grains that appeared on the surface of thepolycrystalline ceramics sintered body.

The numerical values in FIG. 9 and FIG. 10 express the measurementlocation and the measurement number.

Table 5 is a table showing the measurement results in FIG. 9, and Table6 is a table showing the measurement results in FIG. 10.

TABLE 5 Measurement Number 1 2 3 4 5 6 7 8 Langth (μm) 3.187 2.684 1.8541.825 1.563 1.351 1.233 1.643 Measurement Number 9 10 11 12 13 14 15 16Langth (μm) 1.334 0.631 1.498 0.875 0.709 1.252 0.554 0.699 MeasurementNumber 17 18 19 20 21 22 23 24 AVE Langth (μm) 0.698 3.145 2.835 0.6560.789 0.889 2.657 1.666 1.509

TABLE 6 Measurement Number 1 2 3 4 5 6 7 8 Langth (μm) 4.66 6.106 0.8481.016 1.804 1.201 0.437 0.647 Measurement Number 9 10 11 12 13 14 15 16Langth (μm) 1.249 1.11 1.374 2.407 0.656 0.708 0.563 0.898 MeasurementNumber 17 18 19 20 21 22 23 24 AVE Langth (μm) 2.186 1.633 1.406 1.0472.88 2.404 1.032 0.832 1.629

As can be seen from Table 5 and Table 6, the length of the micro recessand the length of the crystal grains that appeared on the surface of thepolycrystalline ceramics sintered body can be said to be approximatelythe same.

This shows that the micro recess is formed to correspond to the crystalgrains that appeared on the surface of the polycrystalline ceramicssintered body.

According to the CMP method that relates to the embodiment, theprotrusion 3 a, the flat part 3 b 2, the recess 13 a, and the recessed13 b can be easily and securely formed. This can be performed such thatthe interference fringe space occupancy ratio to be describedhereinafter becomes less than 1%.

(Quantitative Evaluation Method for Defective Parts)

Next, a description will be given concerning a quantitative evaluationmethod for defective parts such as cracks that reside within the surfaceregion of the dielectric substrate 3.

First, a description will be given concerning defective parts such ascracks that reside within the surface region of the dielectric substrate3.

FIG. 11 is a scanning electron microscope photograph for illustratingcracks generated in the surface region of the dielectric substrate 3.

FIG. 12 is a scanning electron microscope photograph for illustratingthe situation of where a portion of the surface region appears likely todesorb.

When the recessed part 3 a and the planar surface part 3 b are formed byusing a mechanical processing method such as sand blasting, a defectsuch as a crack may occur in the surface region of the dielectricsubstrate 3 as shown in FIG. 11.

When this type of defect resides within the surface region, a portion ofthe surface region appears likely to desorb and may eventually desorb,as shown in FIG. 12.

Examples of generated cracks are those that occur in the crystal grainboundary, those that pass through within the crystal grain boundary, andthose in which these connect irregularly.

Because portions of the surface region that desorb in this manner becomeparticles, it is preferred that defective parts are removed to apredetermined ratio. In order to do this, a quantitative evaluation onthe genesis location of the defect and the degree of incidence(incidence rate) and the like is required.

However, defective parts such as cracks that reside in the surfaceregion of the dielectric substrate 3 are not directly visible from theoutside. In other words, conventionally, a nondestructive quantitativeevaluation for defective parts was difficult.

Next, a description will be provided for a quantitative evaluationmethod for defective parts according to the embodiment.

According to findings obtained by the inventors, photographing thesurface of the dielectric substrate 3 by a laser microscope shows thatportions where defective parts reside have interference fringe. In otherwords, the interference fringe occurs based on the optical path lengthdifference of reflected light from two interfaces, namely, the surfaceof the dielectric substrate 3 and the surface of the defect.

FIGS. 13A to 13C are laser microscope photographs for illustrating whena defect resides in the top face 3 a 1 of the protrusion 3 a. FIG. 13Ais a laser microscope photograph for illustrating the interferencefringe that occurs in the portion where a defect resides; and FIG. 13Bis a scanning electron microscope (SEM) photograph of the cross-sectionon the B-B line in FIG. 13A. Further, FIG. 13C is a magnified photographof the D part in FIG. 13B; and FIG. 13D is a scanning electronmicroscope photograph of the same portion as FIG. 13A.

FIGS. 14A and 14B are laser microscope photographs for illustrating whena defect resides in the flat part 3 b 2 of the planar surface part 3 b.FIG. 14A is a laser microscope photograph for illustrating theinterference fringe that occurs in the portion where a defect resides;and FIG. 14B is a scanning electron microscope photograph of thecross-section on the C-C line in FIG. 14A.

In this case, as shown in FIG. 13D, a defect residing in the surfaceregion can be identified when observed using a scanning electronmicroscope.

Meanwhile, according to the quantitative evaluation method that relatesto the embodiment, a defect such as a crack that is not directly visiblefrom the outside can be identified by interference fringe as shown inFIG. 13A to FIG. 13C and FIG. 14A to FIG. 14B. This means that aquantitative evaluation can be performed nondestructively on thegeneration of defective parts and on their degree of incidence.

The conditions for defective parts can be known based on the size,direction, frequency, and the like of interference fringe.

This type of quantitative evaluation that utilizes interference fringecan be in a manufacturing line for each electrostatic chuckindividually. Therefore, the quality, reliability, and productivity ofelectrostatic chucks can be improved.

Next, further description will be given concerning the quantitativeevaluation for defective parts using interference fringe.

First, the interference fringe is photographed using a laser microscope.

The following can be used as the laser microscope:

Scanning Type Confocal Laser Microscope (Olympus OLS-1100)

Laser Type Ar

Wavelength: 488 nm

Photographic Lens: ×50 Object Lens zoom 1

Optical Mode Non-Confocal

Laser Intensity: 100

Detection Sensitivity: 442

Off-Set: −16

Image: Brilliant Image

Photograph: 8 Accumulated Snapshots

First, the dielectric substrate 3, or the dielectric substrate 3provided on the electrostatic chuck 1, is mounted on the stage of thelaser microscope. Then, the region to be measured (region to bephotographed) is moved directly under the object lens. Next, themagnification of the object lens is selected and the like to determinethe photograph field of view.

Photograph snapshots (8 accumulations) are taken in “nonconfocal mode”.If “confocal mode” is selected, setting the threshold value forextracting the interference fringe is difficult at the time of imageprocess measurement due to the occurrence of uneven brightness. Even in“nonconfocal mode”, sufficient resolution can be obtained.

Next, the image, photographed using the laser microscope, undergoesimage processing (binary coded processing) measurement.

FIG. 15 is a photograph for illustrating the image that has been binarycoded processed.

Note that the bright spot area E in the photograph is the area withinterference fringe.

Image process measurement can be performed using the following imageprocessing software:

Image Processing Software: Win-ROOF (Mitani Corp.)

Binary Coded Processing: 2800-4095

Image Processing Delete 0.2 μm>, Fill in

Measurement: Area Ratio

Next, the quantitative evaluation is performed on the defect based onthe image process measured results.

The quantitative evaluation on the defect can be performed based on theinterference fringe space occupancy ratio (ratio of interference fringeportion area to image area). For example, in the case of FIG. 15, theinterference fringe space occupancy ratio is approximately 0.97%.

According to the findings obtained by the inventors, if the interferencefringe space occupancy ratio, found by using a laser microscope, on themajor surface of the side where the adsorption target material ismounted is less than 1%, then the number of particles generated bydesorption of a portion of the surface region can be greatly reduced.

In this case, defective parts residing in the surface region of thedielectric substrate 3 cannot be removed by buffing. Additionally, thereis the risk of further increasing defective parts if using grindingprocessing methods, laser engraving methods, shot blasting methods, andthe like.

Therefore, in the embodiment, in addition to forming the protrusion 3 a,the flat part 3 b 2, the recess 13 a, and the recess 13 b, removal ofdefective parts that reside up to where the interference fringe spaceoccupancy ratio is below 1% is also performed.

FIG. 16 is a graph for illustrating the conditions for removingdefective parts using a CMP method.

FIG. 17 is a graph for illustrating the conditions prior to removingdefective parts using a CMP method.

FIG. 16 and FIG. 17 show cases in which the dielectric substrate 3 isused in the electrostatic chuck that utilizes a Coulomb force.

An example of the dielectric substrate 3 used in the electrostatic chuckthat utilizes a Coulomb force can be given as that which is formed froma polycrystalline ceramics sintered body, and has an alumina content ofnot less than 99.9 wt %, a bulk density of not less than 3.96, and avolume resistivity of not less than 10¹⁴ Ωcm in the operatingtemperature range of the electrostatic chuck.

In the specification, the bulk density is a value measured by theArchimedes method given in JIS standard (JIS R1634). In this case, thewater saturation method can be a vacuum method, and distilled water canbe used in the solvent.

As shown in FIG. 17, even if the interference fringe space occupancyratio is approximately 3.5% at its maximum, using the CMP methodaccording to the embodiment, the interference fringe space occupancyratio can be made to be less than 1% as shown in FIG. 16.

FIG. 18 is a graph for illustrating the conditions for removingdefective parts using a CMP method.

FIG. 19 is a graph for illustrating the conditions prior to removingdefective parts using a CMP method.

FIG. 18 and FIG. 19 show cases in which the dielectric substrate 3 isused in the electrostatic chuck that utilizes a Johnsen-Rahbeck force.

An example of the dielectric substrate 3 used in the electrostatic chuckthat utilizes a Johnsen-Rahbeck force can be given as that which isformed from a polycrystalline ceramics sintered body, and has an aluminacontent of not less than 99.4 wt % and the volume resistivity of notless than 10⁸ Ωcm and not more than 10¹³ Ωcm in the operatingtemperature range of the electrostatic chuck.

As shown in FIG. 19, even if the interference fringe space occupancyratio is approximately 5% at its maximum, using the CMP method accordingto the embodiment, the interference fringe space occupancy ratio can bemade to be less than 1% as shown in FIG. 18.

In other words, even if the composition of the dielectric substrate 3were to change, the interference fringe space occupancy ratio can bemade to be less than 1% by using the CMP method as described above.

Here, the volume resistivity of the dielectric substrate 3 can becontrolled at the time of firing.

Next, a description will be given of a manufacturing method for thedielectric substrate 3.

First, alumina and titanium oxide are prepared as raw materials. It ispreferred that the alumina and titanium oxide used is that whichparticulates, and the alumina powder used is preferred to have anaverage grain diameter of not more than 0.3 μm and more preferably notmore than 0.2 μm. Meanwhile, the titanium oxide powder used is preferredto have an average grain diameter of not more than 0.1 μm and morepreferably not more than 0.05 μm. Distribution is improved when usingfine granules as raw material making it more difficult for titaniumcompounds with a large grain diameter to segregate.

A preferred lower limit of the average grain diameter for alumina powderis 10 nm. Further, a preferred lower limit of the average grain diameterfor titanium oxide powder is 5 nm.

Next, slurry adjustment, granulating, and raw processing are performed.

A predetermined amount of raw material is weighed and a dispersingagent, binder, and mold releasing agent are added and the mixture iscrushed and stirred by a ball milling. It is preferred that ionexchanged water or the like is used on the mixture so that impuritiesare not introduced. After mixing, granulating is performed by a spraydryer and the obtained granulated powder is press molding so as toprepare a formed body. In addition, it is preferred that CIP molding beperformed on the formed body. CIP molding raises the density of theformed body thereby raising the density of the fired object. Note thatmolding is not limited to dry molding and that the formed body can beobtained by utilizing molding methods such as extrusion molding,injection molding, sheet molding, slip casting, gel cast molding, andthe like.

Next, firing is performed.

The formed body is fired under a nitrogen and hydrogen gas reducedatmosphere to manufacture the dielectric substrate 3.

Reduction firing is performed for titanium oxide to be anonstoichiometry composition thereby enabling the volume resistivity tobe controlled.

For example, by performing firing as given below, the dielectricsubstrate 3 that has the volume resistivity of not less than 10⁸ Ωcm andnot more than 10¹³ Ωcm in the operating temperature range of theelectrostatic chuck can be manufactured.

The firing temperature is preferred to be within the temperature rangeof 1150 to 1350° C. and more preferred to be between 1150 and 1200° C.Firing at a low temperature enables particle growth of the aluminaparticles while also suppressing the growth of segregated titaniumcompounds. Therefore, the maximum particle diameter of alumina particlescan be made to be smaller. Further, the holding time at the maximumtemperature for firing is preferably not less than two hours and morepreferably not less than four hours in order to stabilize the physicalproperties of the fired object.

It is preferred that additional HIP processing is performed on theobtained sintered body. In this manner, a dense dielectric substrate 3can be obtained.

The dielectric substrate 3 can be manufactured according to thedescription given above.

According to the quantitative evaluation method for defective partsaccording to the embodiment, an evaluation method that is nondestructivecan be made on the generation of defective parts and on their degree ofincidence. Based on this quantitative evaluation, the interferencefringe space occupancy ratio can be made to be below the 1%. Moreover,this type of quantitative evaluation can be in a manufacturing line foreach electrostatic chuck individually. Therefore, the number ofparticles generated by desorption of a portion of the surface region canbe greatly reduced. Further, the quality, reliability, and productivityof electrostatic chucks can be improved.

An example was given for quantitatively evaluating defective parts suchas cracks that reside within the surface region of the dielectricsubstrate 3, but quantitative evaluations can also be performed fordefective parts such as cracks that reside in the surface region of thedielectric substrate according to other embodiments. For example,quantitative evaluations can also be performed for defective parts suchas cracks that reside in the surface region of a dielectric substratewhere a protrusion and a planar surface part are formed but the recess13 a and the recess 13 b are not formed, a dielectric substrate with theplate-like shape where a protrusion and a planar surface part are notformed, and the like.

(Average Grain Diameter of Crystal Grains of Polycrystalline CeramicsSintered Body)

Next, a description will be given concerning the average grain diameterof the crystal grains of the polycrystalline ceramics sintered body thatconfigures the dielectric substrate 3.

First, a description will be given concerning the measurement of theaverage grain diameter of crystal grains.

The surface of the polycrystalline ceramics sintered body that is to bethe measurement subject, is given a mirror finish without blemish. Themirror finish can be performed using a diamond wrap method. Moreover,the mirror finished surface undergoes thermal etching. The conditionsfor thermal etching and had a temperature of approximately 1330° C. forapproximately 2 hours of time.

Next, a sputter coating of Au (gold) is applied to the surface. Thethickness of the coating can be approximately 20 nm. A purpose for theAu (gold) sputter coating is to sharpen the contrast in the crystalgrain boundary for when using a laser microscope. In other words, the Au(gold) sputter coating is applied to prevent laser light frompenetrating into the polycrystalline ceramics sintered body. The Au(gold) sputter coating can be performed using an ion sputtering device(Hitachi, Ltd. E-105) or the like.

Next, the thermally etched polycrystalline ceramics sintered body isphotographed using a laser microscope.

The polycrystalline ceramics sintered body is mounted on the stage ofthe laser microscope. Additionally, the region to be measured (region tobe photographed) is moved directly under the object lens. Next, themagnification of the object lens is selected and the like to determinethe photograph field of view.

Photograph snapshots (8 accumulations) are taken in “nonconfocal mode”.If “confocal mode” is selected, setting the threshold value forextracting the crystal grain boundary is difficult at the time of imageprocess measurement due to the occurrence of uneven brightness of thelaser light. Even in “nonconfocal mode”, sufficient resolution can beobtained.

The following can be used as the laser microscope:

Scanning Type Confocal Laser Microscope (Olympus OLS-1100)

Laser Type: Ar

Wavelength: 488 nm

Photographic Lens: ×100 Object Lens zoom 1

Optical Mode Non-Confocal

Laser Intensity: 100

Detection Sensitivity: 400

Off-Set: −30

Image: Brilliant Image

Photograph: 8 Accumulated Snapshots

FIGS. 20A and 20B are photographs for illustrating the polycrystallineceramics sintered body photographed by the laser microscope. FIGS. 20Aand 20B show cases in which the dielectric substrate 3 is used in theelectrostatic chuck that utilizes a Coulomb force. FIG. 20A shows thecase where the average grain diameter of the crystal grains isapproximately 1.8 μm, and FIG. 20B shows the case where the averagegrain diameter of the crystal grains is approximately 1.4 μm.

FIG. 21 is a photograph for illustrating the polycrystalline ceramicssintered body photographed by the laser microscope. FIG. 21 shows thecase where the dielectric substrate 3 is used in the electrostatic chuckthat utilizes a Johnsen-Rahbeck force.

FIG. 21 shows the case where the average grain diameter of the crystalgrains is approximately 1 μm.

Next, the average grain diameter of the crystal grains of thepolycrystalline ceramics sintered body is found based on the imagephotographed using the laser microscope.

The calculation of the average grain diameter of the crystal grains canbe performed using the software given below:

Image Processing Software: Win-ROOF (Mitani Corp.)

Calibration: 0.125 μm/pixels

Background Processing: 12.5 μm/100 pixels

Binary Coded Processing: 2100-2921

Circular Isolation: automatic processing

Measurement: circle equivalent diameter

FIG. 22 is a graph for illustrating the average grain diameter of thecrystal grains and the standard deviation grain diameter distribution.

FIG. 23 is a graph for illustrating the average grain diameter of thecrystal grains and the standard deviation grain diameter distribution.

FIG. 22 shows the case of the dielectric substrate 3 being used in theelectrostatic chuck that utilizes the Coulomb force; and FIG. 23 showsthe case of the dielectric substrate 3 being used in the electrostaticchuck that utilizes a Johnsen-Rahbeck force.

According to the findings obtained by the inventors, as long as theaverage grain diameter of the crystal grains is not less than 0.8 μm andnot more than 1.5 μm, then shedding of crystal grains from the surfaceof the dielectric substrate 3 can be suppressed. As a result, thegeneration of particles can be suppressed. Further, even if sheddingwere to occur, they can be easily removed due to the small size of thegrain diameter which makes it difficult to be held in the concave andconvex parts. Changes in the shape of the protrusion 3 a and the likedue to shedding can be suppressed.

As long as the standard deviation of the grain diameter distribution isnot more than 1 μm, the shedding of crystal grains from the surface ofthe dielectric substrate 3 can be further suppressed. The changing ofthe shape of the protrusion 3 a can be suppressed even if crystal grainsare shed. In this case, controlling the firing conditions enablescontrol of the range of the average grain diameter of the crystalgrains. For example, the growth of the crystal grains may be hindered bycontrolling the firing temperature (for example, approximately 1370°C.), the temperature profile, and the like.

(Depth Dimension of Micro Recesses)

Next, a description will be given concerning the measurement of microrecesses.

The following can be used as the laser microscope.

Scanning Type Confocal Laser Microscope (Olympus OLS-1100)

The following photographing conditions may be used accordingly.

Laser Type: Ar

Wavelength: 488 nm

Photographic Lens: ×100 Object Lens zoom 4.0

Optical Mode Confocal

Laser Intensity: 100

Detection Sensitivity: 400

Off-Set: 0

Image Uptake Mode: three-dimensional uptake (upper and lower limits)

Step Amount: 0.01 μm

Image: Brilliant Image

Photograph: 8 Accumulated Snapshots

Photography may be performed according to the following procedure.

First, the dielectric substrate 3, or the dielectric substrate 3provided on the electrostatic chuck 1, is mounted on the stage of thelaser microscope.

The region to be measured (region to be photographed) is moved directlyunder the object lens.

Next, the magnification of the object lens is selected and the like todetermine the photographic magnification.

The optical mode is set to confocal, and the uptake conditions in theheight direction are set, and the image is photographed.

The measurement conditions for the depth of the micro recess may beaccording to as follows.

Measurement Mode: level difference measurement

Cross-Sectional Direction: horizontal and vertical

Average Mode Line

Cross-Sectional Width: 1

Point: waveform position

FIGS. 24A and 24B are diagrams for illustrating the measurement of thedepth of the micro recess. Note that FIG. 24A is a graph forillustrating the profile of the measurement value; and FIG. 24B is alaser microscope photograph for illustrating the measurement position.

The measurement of the depth of the micro recess may be according to thefollowing procedure.

First, measurement conditions are set in the photograph image.

As illustrated in the examples of FIGS. 24A and 24B, the profiles of themeasurement values in the horizontal direction and the verticaldirection can be scrolled, and not less than 12 points are measured forlocations where there is large asperity within the image. However,defect 100 (formed by shedding) is omitted.

The largest level difference from among the level differences of the notless than 12 measured points is designated as the asperity MAX.

Here, the micro recess 13 a formed in the top face 3 a 1 was found bythe following procedure.

This is performed by a 3 equally distributed pitch (4 measurementimages) toward the periphery from the center of the dielectric substrate3 or the electrostatic chuck 1.

The maximum value from among the MAX value of the asperity leveldifference in each of the measured positions is taken as the depthdimension of the micro recess 13 a formed in the top face 3 a 1.

FIG. 25 is a graph showing the relationship between the depth dimensionof the micro recess 13 a formed in the top face 3 a 1 and the number ofparticles adhered to the underside of the adsorption target material.

The depth dimension of the recess 13 a in samples 1 to 3 was measuredaccording to the photography conditions and measurement conditionsdescribed above.

The depth dimension of the recess 13 a in sample 1 is approximately 150nm; the depth dimension of the recess 13 a in sample 2 is approximately30 nm; and the depth dimension of the recess 13 a in sample 3 isapproximately 20 nm.

When the depth dimension of the recess 13 a is approximately 20 nm, thenumber of particles that adhere to the underside of the adsorptiontarget material was 600 pieces.

In contrast to this, if the depth dimension of the recess 13 a is notless than 30 nm and not more than 150 nm, then the number of particlesthat adhere to the underside of the adsorption target material can benot more than 250 pieces. If the depth dimension of the recess 13 aexceeds 150 nm, then removal of particles that have entered into therecess 13 a becomes difficult.

Therefore, the depth dimension of the micro recess 13 a is preferablynot less than 30 nm and not more than 150 nm.

(Bulk Density and Alumina Content of Polycrystalline Alumina SinteredBody)

The bulk density and the purity (content) of the polycrystallineceramics sintered body that is the base material are critical to formingthe micro recesses 13 a and 13 b when using the CMP method describedabove.

A description will be given here of one example of a polycrystallinealumina sintered body.

FIGS. 26A and 26B are scanning electron microscope photographs of thesurface of the polycrystalline alumina sintered body. FIG. 26A shows thecasw where the average grain diameter of the crystal grains is between20 μm and 50 μm, the bulk density is 3.7, and the alumina content is 90wt %. FIG. 26B shows the case where the average grain diameter of thecrystal grains is not more than 1.5 μm, the bulk density is 3.96, andthe alumina content is 99.9 wt %.

As can be also seen from a comparison of FIGS. 26A and 26B, if the bulkdensity is not less than 3.96 and the alumina content is not less than99.9 wt %, shedding of crystal grains from the dielectric substrate 3can be more securely suppressed because the polycrystalline aluminasintered body that is the base material can have a dense configuration.

In this case, as long as the average grain diameter of the crystalgrains is not less than 0.8 μm and not more than 1.5 μm, then there canbe a dense configuration. There can be a dense configuration as long asat least one of the bulk density or purity (content) is within thepredetermined range. However, it is preferred that both the bulk densityand the purity (content) be within a predetermined range as describedabove. It is more preferred that the average grain diameter of thecrystal grains be not less than 0.8 μm and not more than 1.5 μm. In thiscase, it is preferred that the standard deviation of the grain diameterdistribution be not more than 1 μm as described above.

As long as the polycrystalline ceramics sintered body serving as thebase material has a dense configuration, the micro recesses 13 a and 13b can be uniformly and stably formed using the CMP method as describedabove. As a result, the generation of particles can be greatly reduced.In this case, the bulk density can be controlled by performing HIPprocessing (hot isostatic pressure) or the like. The average graindensity of the crystal grains can be controlled by the firing conditions(firing temperature, firing profile, and the like) as described above.

FIGS. 27A and 27B are schematic diagrams for illustrating the number ofparticles adhered to the underside of a semiconductor wafer. FIG. 27Ashows the case of the polycrystalline alumina sintered body that isserving as the base material shown in FIG. 26A; and FIG. 27B shows thecase of the polycrystalline alumina sintered body serving as the basematerial shown in FIG. 26B.

In the case of FIG. 27A, the number of particles adhered to theunderside of an 8 inch semiconductor wafer is 1058 pieces; and in thecase of FIG. 27B, the number of particles adhered to the underside of an8 inch semiconductor wafer is 67 pieces.

(Other Embodiments of the Electrostatic Chuck)

FIGS. 28A and 28B are schematic cross-sectional views for illustratingthe electrostatic chuck 1 a according to another embodiment. FIG. 28Ashows a schematic cross-sectional view for illustrating theelectrostatic chuck, and FIG. 28B shows a schematic magnified view ofthe F part in FIG. 28A.

In the electrostatic chuck 1 a according to the embodiment, theelectrode 4 is embedded in the dielectric substrate 30.

This type of electrostatic chuck 1 a can be manufactured using, forexample, a green sheet print lamination method and the like.

For example, an electrode may be formed by, first, screen-printing atungsten paste on a green sheet made of polycrystalline ceramicssintered body (for example, a polycrystalline alumina sintered body).Afterwards, to embed the electrode, a plurality of green sheets ispressure laminated to form a stacked body prior to firing. The stackedbody is cut and processed to a desired shape and fired in a reducedatmosphere to enable manufacture of the dielectric substrate 30 with anelectrode embedded therein.

(Method of Manufacturing Electrostatic Chuck)

Next, an illustration will be given of a manufacturing method of theelectrostatic chuck according to the embodiment.

The dielectric substrate 3 provided on the electrostatic chuck can bemanufactured according to the description given above. Because knowntechnology can be applied to the processes relating to the formation,bonding, take up, and the like of each essential element for theelectrode 4 and the like, explanations of these are omitted anddescriptions of only unique processes are given.

FIG. 29 is a flowchart for illustrating the manufacturing method of theelectrostatic chuck according to the embodiment.

First, using a known sand blasting method, the approximate shape of theprotrusion 3 a and the planar surface part 3 b are formed in a majorsurface of the side where the adsorption target material of thedielectric substrate 3 is mounted.

Next, as shown in FIG. 29, the protrusion 3 a, the flat part 3 b 2, therecess 13 a, and the recess 13 b are formed using the CMP methoddescribed above.

At this time, the defect occupancy percentage is found using thequantitative evaluation method for defective parts described above, andCMP processing continues until the defect occupancy percentage reachesnot less than a predetermined value.

In other words, the process continues on the major surface until theinterference fringe space occupancy ratio on the major surface found byusing the laser microscope is less than 1%.

Note that detailed descriptions are omitted because the details thatrelate to the CMP method and the quantitative evaluation method fordefective parts can be similar to those described above.

INDUSTRIAL APPLICABILITY

As described above, according to the invention, an electrostatic chuckthat can suppress the generation of particles and that can easilyrecover a clean state of the electrostatic chuck surface can be providedand has significant advantages to industry.

REFERENCE SIGNS LIST

-   1 electrostatic chuck-   1 a electrostatic chuck-   2 base-   3 dielectric substrate-   3 a protrusion-   3 a 1 top face-   3 b planar surface part-   3 b 1 hole-   3 b 2 flat part-   3 c space-   4 electrode-   10 a power source-   10 b power source-   13 a recess-   13 b recess-   30 dielectric substrate

The invention claimed is:
 1. An electrostatic chuck, comprising adielectric substrate having a protrusion and a planar surface part, theprotrusion being formed on a major surface of the dielectric substrate,an adsorption target material being mounted on the major surface, theplanar surface part being formed in a periphery of the protrusion, thedielectric substrate being formed from a polycrystalline ceramicssintered body, a top face of the protrusion being a curved surface, afirst recess being formed in the top face to correspond to crystalgrains that appear on the surface, the planar surface part having a flatpart, a second recess being formed in the flat part, and a depthdimension of the first recess being greater than a depth dimension ofthe second recess.
 2. The electrostatic chuck according to claim 1,wherein the top face has a curvature radius that is less than acurvature radius of a deformation curve of the adsorption targetmaterial flexed by an adsorptive force.
 3. The electrostatic chuckaccording to claim 1, wherein the depth dimension of the first recessand the depth dimension of the second recess are less than an averagegrain diameter of the crystal grains on the polycrystalline ceramicssintered body.
 4. The electrostatic chuck according to claim 1, whereina side surface of the first recess is a sloped face and an angle betweena bottom surface of the first recess and the side surface of the firstrecess is an obtuse angle, and a portion where the side surface of thefirst recess meets the top face and a portion where the side surface ofthe first recess meets the bottom surface of the first recess are shapedlike a continual roundness.
 5. The electrostatic chuck according toclaim 1, wherein a side surface of the second recess is a sloped faceand an angle between a bottom surface of the second recess and the sidesurface of the second recess is an obtuse angle, and a portion where theside surface of the second recess meets the flat part and a portionwhere the side surface of the second recess meets the bottom surface ofthe second recess are shaped like a continual roundness.
 6. Theelectrostatic chuck according to claim 1, wherein the planar surfacepart has a plurality of holes opening on the planar surface part and theflat part is formed in a periphery of the holes.
 7. The electrostaticchuck according to claim 6, wherein a depth dimension of the holes issmaller than an average grain diameter of the crystal grains on thepolycrystalline ceramics sintered body.
 8. The electrostatic chuckaccording to claim 1, wherein a height dimension of the protrusion islarger than an average grain diameter of the crystal grains on thepolycrystalline ceramics sintered body.
 9. The electrostatic chuckaccording to claim 1, wherein the dielectric substrate is formed from apolycrystalline alumina sintered body and an average grain diameter ofthe crystal grains on the polycrystalline alumina sintered body is notmore than 1.5 μm, and a standard deviation of the grain diameterdistribution is not more than 1 μm.
 10. The electrostatic chuckaccording to claim 9, wherein the dielectric substrate has an aluminacontent of not less than 99.9 wt %, a bulk density of not less than3.96, and a volume resistivity of not less than 10¹⁴ Ωcm in an operatingtemperature range of the electrostatic chuck.
 11. The electrostaticchuck according to claim 1, wherein a curvature radius of the top faceis not more than 20 mm.
 12. The electrostatic chuck according to claim1, wherein the depth dimension of the first recess is not less than 30nm and not more than 150 nm, and the depth dimension of the secondrecess is not more than 30 nm.
 13. The electrostatic chuck according toclaim 9, wherein the dielectric substrate has a volume resistivity ofnot less than 10⁸ Ωcm and not more than 10¹³ Ωcm in an operatingtemperature range of the electrostatic chuck.
 14. The electrostaticchuck according to claim 13, wherein the dielectric substrate has analumina content of not less than 99.4 wt %.